1) Field of the Invention
This invention relates to an integrated circuit used in a photoelectric switch whose principal components, namely, light-receiving elements, an amplifier circuit and their control portions, are formed on an integrated circuit (IC) with reductions in size and pin requirements provided through multifunction circuit arrangements. Also disclosed are improvements in external electrical circuits designed to function cooperatively with such ICs so as to support such multi-function capabilities.
2) Description of the Prior Art
Heretofore, there have mainly been known photoelectric switches of a pulse modulation type in which a photoelectric current produced by a light-receiving element is amplified when a light-emitting diode (LED) is pulse-illuminated to produce pulsating light having a predetermined wavelength which is received as the medium to be detected are only outputted as detection signals. When a detection output is produced in response to pulses of a predetermined level or higher, a light-emitting diode or the like is illuminated in order to make one aware of its output information.
To provide greater flexibility when mounted on machines in operational applications, there is a strong demand for a smaller photoelectric switch. It is therefore desirable to form photodiodes on the integrated circuit (IC) and to reduce the overall size of the IC itself. If one attempts to form the photodiodes and other circuits as an integrated unit and also enhance functions using prior art techniques, the number of IC terminals increases, so that the area necessary for mounting the IC becomes larger than that of the IC chip even if the area of the IC chip itself can be reduced. As a consequence, a contradiction arises in that on an overall basis the photoelectric switch cannot be significantly reduced in size. In addition, a problem arises in that the number of bonding wires, which connect the pins to the IC chip, increases as the number of the pins increase so that there is a high possibility of breaking of the bonding wires, resulting in poorer reliability. Manufacturing cost may also increase due to an increase in the number of steps necessary with additional pin corrections.
In addition, while advances in integrated circuits have improved design flexibility and performance, application to photoelectric switches has been limited. In integrated circuits for photoelectric switches, which are now widespread, light-receiving elements, such as photodiodes for converting light into electrical signals, and their control portions are arranged separately from amplifiers and other circuits. In addition, since it is common in the present art that only one function is assigned to each IC pin correction, even if one attempts to form the photodiodes and the amplifiers in an integrated unit, the number of the pins necessary becomes significantly greater.
Thus, in the conventional photoelectric switch even though multi-function operation may be provided, a terminal for the detection output is provided separately from an output terminal for the light-emitting diode. Accordingly, interconnection of the various circuits requires additional electrical connections. In addition, when an output transistor is unintentionally short-circuited upon wiring, it is apt to result in the failure of the output transistor. In order to avoid such a breakdown, a short-circuit protection circuit is normally provided. However, this circuit is arranged separately from a detection output circuit. Where a further failure such as a disconnection occurs in a light-receiving circuit around a photoelectric element, an amplifier, etc., a self-diagnosing output is sometimes used in order to give this information to an external device. However, a circuit for the self-diagnosing output is also provided in a separated manner and input/output pins are arranged separately from each other.
When a photoelectric switch is employed as a reflection type, a train of pulses is generated by an oscillator so as to flash a projector (a light-emitting diode) at a predetermined time interval and hence to flash the projector at this repetitive period. An interconnected projector means is indispensable for a photoelectric switch of the reflection type, while a switch of a transmission type operates in cooperation with a separate light projector. Thus, it is not practical to flash the separated projector in a synchronized manner. Further, a reflection type photoelectric switch operates with a continuous stream of received photopulses while adjusting or synchronizing the periodicity of the projector with that of a light-receiving unit. On the other hand, in a transmission type photoelectric switch in which the projector is arranged separately from the light-receiving unit it is difficult to adjust the periodicity of the projector with that of the light-receiving unit to provide synchronous operation. For this reason, a non-synchronous type is normally used. If one attempts to produce a general-purpose photoelectric switch, a circuit capable of turning the projector on and off and of selecting either one of the synchronous and non-synchronous operation modes must be provided. In order to do this, a circuit for turning the projector on and off and a circuit for performing the changeover of the synchronous and nonsynchronous operation modes have heretofore been provided in a separated manner. Accordingly, separate input/output pins have also been provided.
Further, a comparator determines whether or not a detection output exists. However, in some cases reliability cannot be assured, for example, in a factory where the atmospheric temperature varies, the level preset as a reference voltage within the comparator varies with such external conditions because of the temperature characteristics of the comparator. In order to avoid such an unreliable state, two voltages having proper levels above and below the reference voltage of the comparator are compared by another comparator to derive a stable state signal. A stable state signal is obtained when the level of the signal becomes equal to or greater than the voltage obtained by that comparison and may be indicated by a displaying means such as a light-emitting diode, for making an observer aware of such a state, whereby the reliability of operation can be monitored. In a reflection-type switch, light is incident upon the light-receiving element when light reflects from a detected object. Whereas, in a transmission type switch no light is incident upon the light receiving elements upon the detection of the object because of the absence of light caused by screening of the object upon detection. Basically, such conditions are just opposite to each other. In a combination switch for reflection or transmission applications it is therefore necessary to permit the changeover between an operational system ("light on") for illuminating an operation indicator upon incidence of light and a system ("dark on") for illuminating the indicator upon screening of light, in accordance with the conditions of actual use. However, in the conventional photoelectric switch, the two functions, i.e., the stable indication function and operation indicating switching function are set in a separated manner and their circuits are also separated from each other.
Furthermore, when the circuit determines whether an object exists, problems arise because of changes in the distance between the object and the light source and because of changes in the brightness of the light source itself. As a result, arrangements for amplifying photoelectric current for use with an active element may include a cumulative amplifying means and a differential amplifying means. However, differential amplifying means is unsuitable for a slight photoelectric current. It is preferable to adopt a high-accuracy differential amplifying means in the presence of a strong photoelectric current. Accordingly, an electric circuit is constructed such that both means can be changed over properly. In addition, an a.c. amplifier for performing amplification of a signal, to the extent that the signal can be processed by a detection circuit, is provided at a stage subsequent to a means for amplifying photoelectric current. It is further advantageous if the gain of the a.c. amplifier can be controlled. Therefore, the amplified signal is controlled by a gain controller but this control is carried out by a circuit different from the above-described amplifying means.
The circuit according to the present invention is designed to employ two light-receiving elements. In this case, two dimensional detection can be performed if the balance of sensitivity between the two light-receiving elements is caused to change, so that the distance to an object to be detected may be changed. For this purpose, it is preferable to provide a circuit for controlling the balance of sensitivity therebetween, but the number of pins becomes greater if such control is performed by means of other pins.
If one attempts to increase the number of functions with conventional circuit construction, the number of the pins is increased by the number of the functions, so that advantageous effects of having a smaller IC with high reliability must be sacrificed. In view of this, it would be desirable to determine ways to provide a number of functions for each pin in order to reduce the number of unnecessary pins, especially upon production of the photo IC.